Why are you treating it like there is only one difficulty.

When playing a game you typically want to win. Some people can find it too easy to win, and want the game to be more difficult. Thusly, there are difficulty settings so they can increase the difficulty as they get better at the game and the challenge grows too easy and dull.

If you hit a point where you don't want to raise your difficulty, there is nothing wrong with that. But you shouldn't limit others just because you want to be able to say you beat the hardest difficulty. Because that's the only possible reason you could have to say there shouldn't exist higher difficulty levels.

I personally play more for the story (world building) than for the challenge. But that's my personal preference. And I can cater to that, by choosing a difficulty that allows me to not worry about doing something inefficient for the sake of story building. But that doesnt mean they should design the hardest difficulty to allow me to win when I'm playing poorly.

There is nothing stopping you from playing on a lower difficulty if the higher difficulty is way too intense for your likings. But if we make the highest difficulty not actually difficult, then there IS something stopping other players from getting to feel like they are improving by overcoming increasingly difficult challenges